Or; put a little brick cleaner in a glass jar, put a "nut"(or anything to keep the part out of the liquid itself)with the part on top in the bottom,screw the lid on and wait until the next day. The fumes will cause a fine rust to form. If the color doesn't match, adjust it (by eye)by letting it stay longer, or rubbing it with steel wool. When the color matches,oil it and rub it up with a piece of cloth.
Mike